The microbiological 7.alpha.-hydroxylation of steroids by means, for example, of Mucor griseocyanus is known and described in Canadian Journal of Microbiology, Vol. 13, pages 1271-1281 (1967). It has now surprisingly been found that a 7.alpha.-hydroxylation of steroids can be carried out with microorganisms of the genus Botryodiplodia, which are entirely different from Mucor griseocyanus.